1. Field of the Disclosure
The invention relates to a thrust reverser unit for a gas turbine engine. In particular, the invention relates to a compact thrust reverser unit for turbofan gas turbine engines.
2. Description of the Related Art
Many modern aircraft use thrust reverser units (TRUs) to assist with the deceleration of an aircraft after landing. Such units operate by reversing the direction of at least a part of the flow passing through the engine, thereby generating a decelerating thrust. TRUs may be used in addition to conventional brakes provided on aircraft wheels. Such conventional brakes may be very efficient, but in adverse conditions, such as a wet or icy runway, the coefficient of friction between the aircraft wheels and the ground may be reduced. In contrast, the effectiveness of the TRUs is unaffected by such adverse conditions.
Conventionally, TRUs are only in use, or deployed, to decelerate the aircraft upon landing. During the rest of the flight, for example during take-off, cruise and decent, the TRUs are stowed away, and represent extra weight. This extra weight leads to increased fuel consumption.
Furthermore, the TRUs also occupy significant space within the gas turbine engine. For example, TRUs conventionally occupy significant space in the nacelle of a turbofan gas turbine engine when they are stowed during flight. It is desirable to reduce the size of nacelles of turbofan gas turbine engines, for example in order to improve the overall efficiency of the engines. The size of current TRUs may not be compatible with the desired reduction in the size of nacelles.
FIG. 2 shows an example of a conventional TRU 50 in both a deployed configuration (shown at the top of FIG. 2), and a stowed configuration (shown at the bottom of FIG. 2). It will be appreciated that, in use, all of the TRU 50 would be either in the deployed configuration or the stowed configuration, and that FIG. 2 shows both the stowed and deployed configurations merely for ease of explanation.
The conventional TRU 50 shown in FIG. 2 comprises a drag link 52, a blocker door 54, a cascade 56, and an actuator 58. In the stowed configuration shown at the bottom of FIG. 2, the blocker door 54, the cascade 56 and the actuator 58 are stowed within the nacelle 60; such that they do not influence the flow 70 through the bypass duct. However, the drag link 52 and its associated joints and hinges, of which there may be several circumferentially spaced around the bypass duct, extends across the bypass duct even when the TRU 50 is in the stowed configuration, thereby causing losses in the flow through the bypass duct.
In the deployed configuration shown at the top of FIG. 2, the actuator 58 has been extended so as to push the cascade 56 and the blocker door 54 rearwards. In doing so, the kinematics of the TRU 50 ensures that the blocker door 54 is rotated so as to extend across the bypass duct. The actuator 58 also moves a portion 62 of the nacelle 60 rearwards so as to expose the cascade 56. Thus, in the deployed configuration, the flow 72 in the bypass duct is prevented for passing along the full length of the duct by the blocker door 54. The cascade 56 then directs the blocked flow out of the engine, through the gap in the nacelle created by the rearward movement of the portion 62 of the nacelle 60, in a direction 74 that has a component in the forward direction, i.e. upstream relative to the flow 72 entering the bypass duct. In this way, the flow through the bypass duct is used to provide a decelerating thrust.